The present invention relates to authenticity determinable printed matter and a method of manufacturing the same.
In a technique used for valuable printed matter such as banknotes, stock certificates, securities, passes, and cards which require anti-forgery and anti-alteration measures, authenticity is determined by checking whether a latent image is visually recognized when printed matter is observed at an angle. Such printed matter uses, e.g., an image line structure of intaglio printed matter, a base member with a three-dimensional pattern and printed image lines, or a change in optical characteristic of ink.
A technique for making a latent image visible by using the image line structure of intaglio printed matter is disclosed in, e.g., Japanese Patent Publication No. 56-19273, in which an image line portion serving as a latent image is formed by using image lines having a large ink layer thickness on intaglio-printed straight lines, and a non-image line portion is formed by using image lines having a small ink layer thickness than the image line portion. When this printed matter is observed while changing the observation angle, the latent image becomes visible because the space between the straight lines is hidden by the image lines having an ink layer thickness in the image line portion at a position ahead of the non-image line portion.
In this technique, however, if observation is done from the direction of straight lines, the latent image is not visible. It is visible only from a direction perpendicular to the straight lines. In addition, since the latent image becomes visible depending on only the height difference between the image line portion and the non-image line portion, it is not easy to visually recognize the latent image.
Japanese Patent Publication No. 56-19273 discloses printed matter in which a latent image becomes visible because the image lines have a uniform width but different directions. In this printed matter, however, the latent image formation position can easily be visually specified. In addition, to make the latent image visible, the observation angle must be large (the printed matter must be tilted largely from the horizontal state). If the latent image should appear at a small observation angle, the ink layer thickness must be large. This is however difficult in producing printed matter.
In an example of printed matter that makes a latent image visible by using a change in optical characteristic of ink, a pattern is formed on the lower surface by gravure printing or silk-screen printing by using ink containing a scaly pigment, as is disclosed in, e.g., Japanese Patent Laid-Open No. 11-11069. According to this technique, the pattern thickness changes depending on the observation angle because of unevenness in scaly pigment distribution. The pattern color also changes. In addition, characters or the like can be added to the pattern. The characters become visible or invisible when the observation angle changes. The lightness (L*) on the base member surface, which is defined by JIS Z8729, falls within the range of 0 to 80 and, preferably, 0 to 45. When the scaly pigment has 1 to 50 wt % and, preferably, 5 to 30 wt % with respect to the ink, the pattern disappearance effect can be made conspicuous.
In this method, however, since the pattern is made visible by changing the pigment distribution density, the density and film thickness on the printed matter become ununiform. For this reason, the pattern is readily visually recognized in a normal state, so the latent image formation position can easily be specified by a third party.
Furthermore, since the pattern that should appear is a simple solid image that is not formed by image lines, only a monotonical pattern is obtained by making the change in color visible or invisible.
PCT(WO) 11-501590 discloses a data carrier having an optical change structure. A three-dimensional pattern is formed on this data carrier by embossing so that the data carrier obtains an optical conversion element with an anti-forgery effect.
In this method, however, embossing is performed after printing on the surface, or printing is performed after embossing. Two steps, printing and embossing, are necessary. In addition, a shift may occur between an embossing position and a printing position.
Furthermore, embossed traces remain even on the lower surface of the embossed printed matter. This adversely affects the image pattern on the lower surface. Moreover, when some pressure is applied to the printed matter, the embossed portion is lost, and hence, the visual embossing effect is lost.
An example of conventional printed matter makes a latent image visible by using a base member having a three-dimensional pattern and printed image lines. For example, Japanese Patent No. 2615401 by the present applicant discloses printed matter which uses a material on which various kinds of straight lines or relief representing an image pattern, or both of them are formed by embossing. Image lines made of various kinds of straight lines or image lines made of halftone dots having a predetermined interval, or image lines of both types are printed on the material to be parallel or have an angle to a portion except the above-described three-dimensional image pattern by using color inks except the ink of the color of the material or colorless ink.
According to this printed matter, when it is observed from the front, the image lines made of various kinds of straight lines or image lines made of halftone dots, which are formed by straight lines at a predetermined interval, or the image lines of both types are confirmed. When the printed matter is observed from an oblique direction, the three-dimensional image pattern is easily be confirmed depending on the positional relationship between the three-dimensional pattern and the printed image lines having a predetermined interval. When the printed matter is observed from a reverse oblique direction, the image pattern with its bright and dark portions inverted is confirmed.
In this printed matter, however, embossing is performed after printing on the surface, or printing is performed after embossing. This technique also requires two steps, i.e., printing and embossing.
In printed matter disclosed in Japanese Utility Model Laid-Open No. 05-76765, a solid polarizing ink layer containing pearl pigment is printed on the entire surface of a base member sheet. An abstract image pattern or character pattern made of an aggregate of straight or curved lines is printed on the polarizing ink layer by using color inks. Light that becomes incident from the upper surface side is periodically reflected in a predetermined direction by the pearl pigment in the polarizing ink layer to generate a gloss. Simultaneously, the abstract image pattern or character pattern printed by the color inks becomes visible.
In such printed matter, the line drawing is printed by using a normal ink. Hence, the printed matter may be copied, and the latent image effect is insufficient.
Printed matter disclosed in Japanese Patent Laid-Open No. 11-11069 makes a pattern visible by changing the pigment distribution density and ink layer thickness between the background portion and the character portion contained in the pattern. In this technique, since the density and film thickness on the printed matter become ununiform, the latent image formation position can easily be confirmed by a third party. If image lines with thicknesses are printed by using an ink mixed with a normal scaly pigment, the pigment may settle to lose the effect of the scaly pigment. In some cases, the latent image disappears, or its appearance is not conspicuous. In addition, the lightness of the base member must be limited.
In the above prior arts, the latent image does not change from a negative image to a positive image or from a positive image to a negative image depending on the observation angle or observation direction. Hence, the anti-forgery effect is insufficient.